A web page may display content items. An advertisement is an example of a content item. Selection of the content items may be based on numerous factors, including, e.g., age, gender, profession, and income level of a viewer of the web page.
In an example, the web page includes content. In this example, the content may also be used in selecting the content items, e.g., by selecting content items that are relevant to the content in the web page.